Are you importing a .blend file?
Just got to File>>Append.
A file browser will appear in the 3d window.
The buttons ‘-’ (drive selector) and ‘P’ (Move to parent directory) are for directory navigation.
Find your directory and .blend file. Select the category of elements you want to append to your current file. IE Object, Material, etc. (Scene will append entire scenes)
Select elements. Left click for one item, Right click to select more items.
Click Load Library. All elements should be in the same layers as in the old file.